Generally, each crank arm is provided with a through bore through which the pedal shaft is fixed thereto mainly by a screw means.
In a racing bicycle, a length between the axis of the crank shaft and the axis of the pedal shaft is determined by the strength of a driver's legs for a pedalling operation. In a conventional bicycle this depends upon the bicycle size.
Conventionally, to provide differing crank arm lengths required the production and stocking of many crank arms of different lengths.
To alleviate the requirement for producing and stocking many crank arms of differing lengths, the inventor has developed a novel crank means wherein the crank arm length is adjustable comprising a crank arm which is provided at the utmost end for mounting the pedal with a through bore larger in diameter than the pedal shaft, an adapter having an eccentric bore for mounting the pedal shaft and at the outer periphery of one axial end a flange larger in diameter than the through bore and at the outer periphery of the other axial end a screw thread, and a nut screwable therewith, so that the adapter is non-rotatably fitted into the through bore but is shiftable in a desired circumferential position and screwed with the nut to be mounted into the through bore.
This crank means, while providing an adjustable length crank arm, is deficient in that the nut loosens by vibrations or impacts during the bicycle's running to produce a gap between the nut and the crank arm so that the adapter, and in turn the pedal supported thereto, is loosened, resulting in the danger of careless separation of the pedal from the crank arm.